UefiPayloadPkg: Add PCD_DYNAMIC_AS_DYNAMICEX and set to True

PCD_DYNAMIC_AS_DYNAMICEX is recently added to Edk2, and it can treat
Dynamic PCD to Dynamic Ex PCD, which is Uefi Payload needs.

Cc: Guo Dong <guo.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Maurice Ma <maurice.ma@intel.com>
Cc: Benjamin You <benjamin.you@intel.com>
Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>

UefiPayloadPkg/UefiPayloadPkg.dsc

@@ -24,6 +24,7 @@
   SKUID_IDENTIFIER                    = DEFAULT
   OUTPUT_DIRECTORY                    = Build/UefiPayloadPkgX64
   FLASH_DEFINITION                    = UefiPayloadPkg/UefiPayloadPkg.fdf
+  PCD_DYNAMIC_AS_DYNAMICEX            = TRUE
 
   DEFINE SOURCE_DEBUG_ENABLE          = FALSE
   DEFINE PS2_KEYBOARD_ENABLE          = FALSE